In arc welders and plasma cutters, it has become common practice to use switching power supplies of the inverter type. An output transformer includes two separate sections of the primary winding, each section of which is alternately provided with current pulses in opposite directions to create an AC output rectified and used for electric arc welding or plasma cutting. Various types of inverters are employed, such as a push pull inverter wherein the primary winding is divided into two sections and a single DC power supply is used to switch current pulses in one direction through one section of the primary and then in the opposite direction in another section of the primary. By alternately switching the current pulses through the primary sections, AC current is developed. Such push pull type inverters are operated at a frequency of at least 20 kHz with a single switch for each primary used for creating opposite polarity current pulses in the sections of the primary winding. The electric arc welding and plasma cutting requires high energy with wattage well over 500-1,000 watts. Indeed, inverters used as the power supply for electric arc welding and plasma cutters often have input currents well over 60 amperes and voltages over 200 volts. When using such high energy switching type power supplies, it is the practice of The Lincoln Electric Company in Cleveland, Ohio, a leading manufacturer of electric arc welders and plasma cutters, to provide an inverter with one primary winding section connected to a DC first power source and the other winding connected to a second DC power source. These power sources can be connected in series or in parallel to cover the range of potential voltages, i.e. 200-275 volts. When using such high energy inverters for creating the AC primary signal, two switches are operated in unison for each of the two primary winding sections. One set of switches is closed to create a current pulse in one direction through one section of the primary. Thereafter, a second set of two switches is closed to create a current pulse in the opposite direction to the other section of the primary winding. Each of these sections is driven by its own DC voltage source having an input filter capacitor that maintains the input terminals of both switching networks at a fixed voltage. To allow voltage balancing and interconnecting of the two primary sections, each primary section is clamped to its input power supply by a clamping diode connecting the bottom of the section to the positive terminal of the power supply. The top of the winding section is clamped to the ground of negative terminal of the power supply. Each of the switches in the inverter, which operate at a high rate exceeding about 20 kHz, is provided with a dissipating snubber including a capacitor and resistor in series and connected across the switch in parallel. High voltages caused by the transformer leakage inductance during the opening of the switches contain energy which is clamped to the power supply and is also dissipated around the switches to reduce the necessary rating of the individual switches. These standard snubbers are large, heavy and dissipate a large amount of heat to decrease the efficiency of the electric arc welder or plasma cutter. Substantial research and development has been directed to reducing the size of these snubbers and providing more effective snubbing networks for decreasing the size, cost and weight of the snubbers necessary to protect the high speed switches demanded for power supplies used in the welding industry. However, the only snubbers which have had the capability of absorbing the energy created by high energy power supplies have been the dissipating, passive type. Such snubbers are now universally used in the welding industry.
There are a number of snubber networks which employ non-dissipative voltage snubbers; however, they have been heretofore used for low power devices generally less than about 200 watts. In addition, these snubbers require the use of relatively large inductors to polarize the snubber network. For this reason, there has been no impetus for, or knowledge of, employing passive, non-dissipative snubber networks in high energy power supplies of the type needed for electric arc welding and plasma cutting.